Electrical resistor device



Feb. 9, 1965 M. A. THOM C ELECTRICAL RESISTOR DEVICE Original Filed Nov. 6, 1958 INVENTOR,

MELVIN A. THOM wa flwr FIG.4

his attorneys.

3,169,237 ELEETRICAL RESHSTOR DEVICE Melvin A. Thom, 410 Ponce de Leon, Clearwater, Fla.

flontinuation of application Ser. No. 772,368, Nov. 6,

1958. This application Jan. 4, 1963, Ser. No. 249,531 8 Claims. (*Ci. 33il-253) This invention relates to resistor devices for inclusion in electrical circuits in uses in which light weight, compact size and efficient dissipation of heat for any given capacity are important requirements, as in the equipment employed in aviation, communications and like fields. My prior Patent No. 2,558,798 disclosed sucha resistor comprising a wire resistance element wound upon a core or spool of porcelain and insulated and enclosed in a metal housing adapted for installation on the instrument panel of equipment to be served. While the device of my prior patent has proven successful in practical use, my present invention is an improvement over such prior device in several important respects.

One object of the present invention is to provide an improved resistor device oftheabove character, of less size and weight and operating at a lower temperature for any given capacity in watts.

Another object is the provision of such a device com- 7 prising an improved metallic housing forthe resistance unit so constructed as to more efficiently withdraw the Patented Feb. 9, 1965 extending threaded bore 26 to receive an attaching screw or stud 22 inserted through an opening in the panel 18,

as shown, for drawing the housing down and holding it in rigid and intimate contact with the panel, thus providinga simple and practically convenient means for supporting the housing on the panel in eificient heat-conducting relation therewith.

The electrical unit proper comprises a ceramic or porcelain core 24 of generally sleeve-like shape, the opposite ends of the outer surface of which have fixed thereon the electrically conducting metal anchoring rings 26, as

shown; The electrical resistance element or wire 28 is then wound directly on the core between the rings, with the ends of the winding soldered or otherwise electrically otherwise electrically connected to the other ring 26, turned partly inwardly across the core and extended in heat generated in the resistance unit and distribute it adapted for more etiicient and convenient'attachment to,

an instrument panel or other support. 1

Still a further object is to supply a resistor device havan axial direction. The winding and rings are then coated with a suitable resin varnish, plastic or other electrical insulating material 29 such, for example, as the silicone varnish known as Dow Corning 805, manufactured by Dow Corning Corporation of Midland, Michigan, which 1 A flat, washer-like mica member 34 having its outer ing the above advantages in a more practical and'economical type of construction.

To these and other ends the invention resides in certain improvements and combinations of, parts, all as will be hereinafter more fully described, the'novel features being pointed out in the claims at the end of the specification.

In the drawings: 1

FIG. 1 is a side elevation of a resistor device embodying the present invention; t

FIG; 2 is a top plan view of the same;

FIG. 3 is a bottom plan view of the same;

FIG. 4 is an enlarged sectional elevation on the line 44 in FIG. 2, and

FIG. is an enlarged sectional elevationon the line 5-5 in FIG. 2.

The present invention resides in a number of novel features, such as an improved metal housingof more com-- pact and thermally efiicient construction, improved means for supporting and insulating the electrical resistance unit therein and means for mounting the housing on an instrument panel or other support, as more fully specified in the appended claims. The embodiment, herein disclosed byway of illustration, preferably comprises ahousing of aluminum or other suitable heatconducting metal,

12. The bottom wall has a fiat bottomsurface' as shown for mounting in intimate contact with the surface of a metal instrument panel or other support 18 such, for

example, as the instrument panel of an airplane; Bottom wall i2-and post '16 are formed centrally with an upwardly outer walll' i but also the inner body or post 16 is in;

and inner diameters closely fitting the inner diameter. of wall 14 and the outer diameter of the post 16, respectively, is laid on the bottom wall 12 atthe bottom of the opening between the wallaud post. A sleeve 38 of woven glass fibers, such as Fiberglas, is fitted closely over the length of the post and a similar sleeve 36 is closely fitted to, the inner surface of the outer wall. T he'sesleeves are saturated with the silicone varnish referred to above and may be allowed to air-dry at room temperature'for half an hour until the saturating varnish acquires a tacky state.

The resistor unit, comprising the porcelain core, winding and leads, is inserted into the space or annular recess 46 between the said sleevesand all the remaining space between the wall 14 and post 16 is filled with the said silicone varnish, care being taken to insure thatthe space in the housing about the resistor core is completely filled with the said insulating varnish, free from air pockets. The varnish is then allowed to air-dry as described above to allow all solvent to escape, after which the device is baked, starting at room temperature and raising the temperature gradually up to 250C. over a period of ten hours. Then it is further baked for one andone half hoursat a temperature of 250 C. As shown, the resi'stor' core and its winding parts are completely. enclosed .and insulated by the sleeves and insulating varnish, except 1 forthe projecting ends of the terminals 30 and 32.

The above described resistor may obviously be made in a wide range of sizes for different power loads, one successful size, for example, of 50 watts capacity, having. a p housing with an outside diameter of11/16of an inch and an axial length of /sof an inch. The minimum thickness of the bottom wall 12' and the thickness of the the inner post 16 is of an inch.

The "invention thus provides a principle Qf construction by which the heat generating winding 28 audits insulating materials are disposedin direct, heat -conducting contact with the metal housing on all sides except only at the open end of the housing. Not onlythe 3 contact with the coil and its insulation throughout the circumference of the latter and post 16, like outer wall 14, is in integral and efficient heat-conducting continuity with the metal bottom wall. 12 for transferring the heat through direct and ample contact with a metal instru-,

ment panel or support 18, by which the heat is distributed and further dissipated. Such complete contact between the metal housing and substantially all surfaces of the electrical unit has been found to effect a surprisingly increased reduction in the heating of the unit under operating loads. It has been further found that this construction tends to maintain a more uniform temperature from end to end of the electrical winding and its insulation.

Furthermore, this principle of construction facilitates a proportioning of the dimensions of the device which has been found to further materially increase its operating efliciency. That is, the efficient heat-conducting construction described above is compatible with a limitation of the length, aximly of the winding and housing, inrelation to their diametrical dimensions. I have found that the temperature of the coil and its insulating materials is kept lower by restricting the axial length to about the diameter, or not more than one and one half times the diameter, as in the dimensions given above. Such advantageous characteristics supply a resistor of materially lessened size and increased ability to operate under relatively heavy loads without excessive heating or. damage.

The arrangement of the encircling side wall 14 and inner post 16 in efiicient conducting relation, through bottom wall 12-, with a supporting panel 18, is further advantageous in limiting the area of contact with the support and thus adapting the device for use with small panels, or where the available panel space is restricted.

A resistor embodying the present invention, as compared, for example, with a resistor of my Patent No. 2,558,798, having an equivalent electrical winding and diameter, occupies about one-third the length and cubical content, for the same capacity in watts and the same conventional temperature rise to not more than about 275 C. The present construction, moreover, is better adapted for production by more convenient and economical materials and methods.

This application is a continuation of my pending application, Serial No. 772,368, filed Nov. 6, 1958, now abandoned.

It will thus be seen that the invention accomplishes its objects and while it has been herein disclosed by' reference to the details of a preferred embodiment, it is to be understood that such disclosure is intended in an illustrative, rather than a limiting sence, as it is contemplated that various modifications in the construction and arrangement of the parts will readily occur to those skilled in the art, within the spirit of the invention and the scope of the appended claims.

I claim:

1. A resistor device for electrical circuits comprising.

an integral metal housing having an inner substantially solid post and an outer side wall and a bottom wall, with said side wall extending from said bottom wall in substantially coextensive spaced relation to said post to provide a recess therebetween open at one side of said device and closed at the opposite side by said bottom wall, a resistor unit housed in said recess and comprising a core of electrically insulating material having a resistance element thereon, terminal leads extending from said element externally of said device above said bottom wall, electrical insulating material entirely surrounding and enclosing said core and element and filling the space between the same and said post and side and bottom walls, and a screw threadedly engaging said bottom wall and post for securing said bottom wall of said device .to a thermally conductive support for distributing and '4 dissipating heat from said unit and insulating material to said support.

2. A resistor device of fixed capacity for'electrical circuits comprising an integral heat conductive metal housing having a bottom wall, a substantially solid post extending normally thereto at the center thereof and a side wall on said bottom Wall surrounding said post, said post and side wall being substantially coextensive and spaced apart to form therebetween a receiving space opening outwardly at the side of said device opposite said bottom Wall, a resistor unit housed in said space and comprising an insulating core having a resistance element wound thereon, electrically insulating plastic material entirely surrounding and enclosing said core and element and filling the space between the same and said post and side wall, and means for securing said device to a thermally conductive support for distributing and dissipating heat from said unit and insulating materials to said support and surrounding atmosphere.

3. A resist-or device of fixed capacity for electrical circuits comprising a substantially cylindrical, integral metal housing having a flat bottom wall, a post extending normally thereto at the center thereof and a side wall on said bottom wall surrounding and spaced from said post to form therebetween a receiving spaced opening outward- 1y, at the side of said device opposite said bottom wall, a resistor unit housed in said space and comprising an insulating core having a resistance element wound circumferentially thereon, electrical insulating material surrounding said core and element and filling the space between the same and said post and side wall, terminal leads extending (from said element through said insulating material and externally of said device above said bottom wall, and means for securing said device to a thermally conductive support for distributing and dissipating heat from said unit and insulating materials to said support.

4. A compact, light-weight electrical resistor adapted to operate at a substantially fixed resistance value, said resistor comprising: a heat conductive metal housing formed with a flat bottom, a substantially solid, generally cylindrical, center post normal to and in thermally conductive relation with said bottom, and a solid outer wall in thermally conductive relation with said bottom and surrounding said post to define a recess between said post and said outer wall; a generally cylindrical, hollow, resistor coil housed in said recess and dispose-d so that each of the turns of said coil encircles said post; terminal leads extending from said coil; electrical insulating material wholly surrounding and enclosing said coil and filling the space in said recess thereabout; and means for securing said housing bottom to a thermally conductive support for conducting and dissipating heat from said unit to said support, whereby said unit normally operates below a relatively low maximum temperature.

5. An electrical resistor as specified in claim 4 in which said resistor unit and said insulation thereof are completely enclosed in said recess and in intimate heat conducting contact with said outer wall, said inner post, and said bottom of said housing.

'6. A compact, lightweight electrical resistor adapted to operate at a relatively low temperature and comprising: a substantially solid housing of heat conducting metal with a flat bottom and an annular recess extending inwardly fnom the top of said housing and into proximity with said bottom, said annular recess defining a substantially solid, generally cylindrical, central post normal to said bottom and a substantially solid outer wall surrounding said post; an electrical resistance unit housed in said recess and comprising a hollow, cylindrical core of electrically resistant material having wound thereon a resistance coil, said hollow core and coil surrounding said post so that each of the turns of said coil encircle said post; terminal leads extending from the opposite ends of said coil; electrical insulating material wholly the space in said recess thereabout to exclude air pocketsj' and means for securing said housing bottom to a support for conducting and dissipating heat from said unit and housing to said support, whereby said unitmaintains a relatively uniform operating temperature throughout said coil.

7. An electrical resistor of fixed resistance value com prising a heat conductive integral metal housing of substantially solid cylindrical shape formed with a fiat bottom and with a concentric annular recess extending to adjacent said bottom and opening outward at the top of said housing, said recess being located adjacent the periphery of said housing and defining a substantially solid central post normal to said bottom and surrounded by a peripheral wall of said housing, said housing having a diameter and length in the ratio of notless than about two to three; a resistor unit housed in said recess and comprising a hollow, generally cylindrical core having wound thereon a resistance coil each turn of which encircles said post; terminal leads extending from said coil outward through the top of said housing recess; electrical insulating material wholly surrounding and enclosing said core and coil and filling the space in said recess 'thereabout; and means for securing said housing bottom to a thermally conductive support for conducting and dissipatingheat from said unit to said support whereby said unit normally operates below a relatively low maximum temperature.

8. An electrical resistor of fixed ohmic value adapted for use in an electric circuit, said resistor comprising a heat conductive metal housing of substantially solid, cylindrical shape formed with a fiat bottom and with a concentric annular recess extending to adjacent said bottom and opening outward at the top of said housing, said recess defining a substantially solid central post normal to said bottom and surrounded by a substantially solid peripheral wall of said housing; a resistor unit completely enclosed in said recess and comprising a hollow, generally cylindrical, core of electrically resistant material having wound thereon a resistance coil each individual turn of which encircles said post; conductive metal anchoring rings on the end of said core and connected to the ends of said coil respectively; terminal leads extending from said anchoring rings; a ring of insulating material between the bottom of said recess and said coil; sleeves of insulating material between the sides of said recess and said core and coil; electrical insulating material Wholly surrounding and enclosing said'core and coil and filling the space between the same and said insulating ring and sleeves; and means for securing said housing bottom to a thermally conductive support for conducting and dissipating heat from said unit to said support, whereby said unit normally operates below a relatively low temperature.

References Cited in the file of this patent UNITED STATES PATENTS 1,007,000 Gold Oct. 24, 1911 2,039,760 Wiegand et al May 5,1936 2,204,623 Ruben June 18, 1940 2,355,680 Ruben Aug. 15, 1944 2,369,045 Humpton et a1 Feb. 6,1945 2,558,798 Thom July 3, 1951 2,596,503 Newnham May 13, 1952 2,619,571 Ganci Nov. 25, 1952 2,907,860 Geller Oct. 6, 1959 FOREIGN PATENTS 405,611 Great Britain Jan. 22, 1934 583,466 Canada Dec. 16, 1958 

4. A COMPACT, LIGHT-WEIGHT ELECTRICAL RESISTOR, ADAPTED TO OPERATE AT A SUBSTANTIALLY FIXED RESISTANCE VALUE, SAID RESISTOR COMPRISING: A HEAT CONDUCTIVE METAL HOUSING FORMED WITH A FLAT BOTTOM, A SUBSTANTIALLY SOLID, GENERALLY CYLINDRICAL, CENTER POST ORMAL TO AND IN THERMALLY CONDUCTIVE RELATION WITH SAID BOTTOM, AND A SOLID OUTER WALL IN THERMALLY CONDUCTIVE RELATION WITH SAID BOTTOM AND SURRROUNDING SAID POST TO DEFINE A RECESS BETWEEN SAID POST AND SAID OUTER WALL; A GENERALLY CYLINDRICAL, HOLLOW, RESISTOR COIL HOUSED IN SAID RECESS AND DISPOSED SO THAT EACH OF THE TURNS OF SAID COIL ENCIRCLES SAID POST; TERMINAL LEADS EXTENDING FROM SAID COIL; ELECTRICAL INSULATING MATERIAL WHOLLY SURROUNDING AND ENCLOSING SAID COIL AND FILLING THE SPACE IN SAID RECESS THEREABOUT; AND MEANS FOR 